The present invention relates to a head box for a paper machine for continuously feeding the papermaking slurry onto the endless forming wire cloth or fabric which is rotated.
In order to obtain a sheet of paper which is uniform in the widthwise direction and has a high degree of strength in the lengthwise direction, papermaking slurry must be fed such that fibers in the slurry are spread to prevent flocking thereof and that the fibers are oriented in a direction of the papermaking slurry flow.
In view of the above, there has been proposed an arrangement as shown in FIG. 19 in which a plurality of papermaking slurry feed tubes 2 are disposed in parallel with each other within a head box 1 and a ribbon-shaped twisted plate 3 is fitted into each tube 2 so that the slurry flowing through the tube 2 is caused to swirl (Japanese Patent First Publication No. 93895/1980). The slurry discharged out of the respective slurry tubes 2 is joined and caused to issue through a slice outlet 4 onto a wire cloth or fabric 5. When an ordinary papermaking slurry having a low concentration is fed through the head box 1 of the type described above onto the wire cloth or fabric 5, the fibers in the slurry are satisfactorily dispersed, uniformly spread in the widthwise direction and oriented in a direction of travel of the wire cloth or fabric 5.
However, when a highly concentrated papermaking slurry is supplied to the head box 1, the slurry cannot be dispersed satisfactorily and it is not possible to make uniform paper. For highly concentrated slurry, not only strong agitation is necessary, but also agitation should be kept to the vicinity of the slice outlet, because the slurry causes re-flocking in very short time. If the head box shown in FIG. 19 is used, for satisfactory dispersion of fiber, it is necessary to adopt very high flow velocity through the tubes. However the high velocity causes large-scale turbulence at outlet of tubes and causes streak at slice outlet. In order to stabilize the turbulence, long distance between tube outlet and slice outlet is necessary and this results that slurry easily flocks again.
When the slurry tube 2 is reduced in diameter so as to suppress the disturbance of the discharged slurry, there arises the problem that the slurry clogs the slurry tube 2.
The present invention was made to overcome the above and other problems encountered in the conventional paper machines and has for its object to provide a head box which can cause a papermaking slurry even at a high concentration to swirl sufficiently so that a sheet of paper having a uniform quality in the widthwise direction and a high degree of strength in the lengthwise direction can be fabricated.